[rubyfmt](https://github.com/fables-tales/rubyfmt) is a formatter for
`ruby` code.
This commit adds support for `rubyfmt` as a `ruby` fixer (#2991),
together with some tests and documentation.
Nickel(https://nickel-lang.org/) is a configuration language, like
Jsonnet, Cue, Dhall.
`nickel`(https://github.com/tweag/nickel) is the main command to run,
export and also format Nickel code.
this commit adds `nickel format` as a Nickel fixer, together with some
tests and documentation.
this commit adds refurb as a Python linter, together with some tests
and documentation. it should fix issue: #4362
refurb repo: https://github.com/dosisod/refurb
`checkmake` by default checks config file "in the same folder it's
executed in" unless `--config` option is set.
This commit allows setting the `--config` option with an option
variable (with documentation updated).
Yining